Barrier layer for inflatable structures

ABSTRACT

An air-impermeable fabric is disclosed. The air-impermeable fabric has a fabric substrate, which may also be referred to as a base fabric. Disposed over the fabric substrate is a barrier layer comprising a polymer binder and at least 20 weight percent graphene nanoplatelets, based on the total weight of the barrier layer. A barrier underlayer, which may or may not also include graphene nanoplatelets, is disposed between the fabric substrate and the barrier layer. A barrier overlayer, which may or may not also include graphene nanoplatelets, is disposed on the opposite side of the barrier layer from the barrier underlayer

This is a continuation-in-part of U.S. patent application Ser. No.13/490,083, filed Jun. 6, 2012, the disclosure of which is incorporatedherein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to air-impermeable fabrics, and moreparticularly, to fabrics used for emergency evacuation equipment foraircraft evacuation such as evacuation slides and life rafts, as well asother inflatable structures such as for cushions and other emergency andnon-emergency applications.

The requirement for reliably evacuating airline passengers in the eventof an emergency is well known. Emergencies at take-off and landing oftendemand swift removal of the passengers from the aircraft because of thepotential for injuries from fire, explosion, or sinking in water. Aconventional method of quickly evacuating a large number of passengersfrom an aircraft is to provide multiple emergency exits, each of whichis equipped with an inflatable evacuation slide, which often doubles asa life raft in the event of a water evacuation. These evacuation slidesare most commonly constructed of an air-impervious coated fabricmaterial that is formed into a plurality of tubular members. Wheninflated, these tubular members form a self-supporting structure with aslide surface capable of supporting the passengers being evacuated. Inaddition to being air-impervious, the fabric material from which thetubular members are constructed must meet FAA specification requirementsof TSO-C69c for resistance to radiant heat, flammability, contaminants,fungus and other requirements.

Although evacuation slides permit passengers to quickly and safelydescend from the level of the aircraft exit door to the ground, therequirement that each aircraft exit door be equipped with an inflatableevacuation slide means that substantial payload capacity must be devotedto account for the weight of multiple evacuation slides. Accordingly,there has long existed the desire in the industry to make the inflatableevacuation slides as light as possible. A significant portion of theweight of an emergency evacuation slide is the weight of the slidefabric itself Accordingly, various attempts have been made to reduce theweight of the slide fabric. One accepted method has been to reduce thephysical size of the structural members of the slide by increasing theinflation pressure. Increased inflation pressure, however, causesgreater stress on the slide fabric and, therefore, the benefit of thereduced physical size is at least partially cancelled out by the need touse a heavier gauge of slide fabric in order to withstand higherinflation pressures. Current state of the art slide fabric consists of a72×72 yarns per inch nylon cloth made of ultra-high-tenacity nylonfibers. This 72×72 fabric by itself has a grab tensile strength ofapproximately 380 lbs in the warp direction and 320 lbs in the filldirection (as used herein grab tensile strength refers to the strengthmeasured by grabbing a sample of fabric, typically 4 inches wide,between a set of one inch wide jaws and pulling to failure.) The fabricis typically coated with multiple layers of an elastomeric polymer torender it impermeable to air as well as a radiant-heat-resistantcoating. This results in a strong, but heavy fabric, having a grabtensile strength of approximately 390 lbs in the warp direction and inthe fill direction, but with an areal weight that can exceed 7.0 oz/yd².As can be determined from the foregoing, these coatings do notcontribute significantly to the strength of the fabric.

Although the above-described fabrics for inflatable structures haveachieved widespread use in the aviation industry, the disparaterequirements for strength, weight, and flame resistance, as well asother requirements, have resulted in a continuing need in the art fornew fabrics.

BRIEF DESCRIPTION OF THE INVENTION

As described in further detail below, the invention provides a newair-impermeable fabric. The air-impermeable fabric has a fabricsubstrate, which may also be referred to as a base fabric. Disposed overthe fabric substrate is a barrier layer comprising a polymer binder andat least 20 weight percent (wt. %) graphene nanoplatelets, based on thetotal weight of the barrier layer. A barrier underlayer, which may ormay not also include graphene nanoplatelets, can optionally be includedbetween the fabric substrate and the barrier layer. A barrier overlayer,which may or may not also include graphene nanoplatelets, is disposed onthe opposite side of the barrier layer from the barrier underlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of an air-impermeable fabric asdescribed herein;

FIG. 2 is a side view of an aircraft evacuation slide as describedherein;

FIG. 3 is a bottom view of an aircraft evacuation slide as describedherein; and

FIG. 4 is a graph plot of air permeation through fabrics as describedherein.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, the invention is directed to an air-impermeablefabric. It should be noted that, as used herein, the term “impermeable”does not refer to absolute or permanent impermeability, but rather to adegree of permeability sufficiently low to meet the functionalrequirements needed for any particular inflatable application. Thefabric substrate, or base fabric, can be formed from any type of fiberpossessing desired physical properties and processability. Nylon fibersare often used, at least in part due to the strength and strength toweight ratio possessed by nylon fabrics. Various nylons, such asnylon-6,6 or nylon-6, can be used, as well as other known nylonpolymers. Other polymer fibers can also be used, such as polyester,other aromatic and/or aliphatic polyamides, liquid crystal polymers,etc. Natural fibers such as silk can also be used. Fiber diameters canbe selected to achieve desired properties such as fiber spacings inwoven fabric. Yarn counts can range from 30×30 yarns per inch to 90×90yarns per inch, or higher, and more particularly from 40×40 yarns perinch to 75×75 yarns per inch. The yarn count geometry can also beasymmetric (i.e. 40×60 yarns per inch) if needed.

The fiber strength of the base cloth can also be increased byincorporating nanoreinforcements into the polymeric matrix of the fiberitself The nanoreinforcements can be carbon nanotubes, carbonnanofibers, graphene nanoplatelets, polymeric nanofibers, metallicnanotubes or nanofibers, metal oxide nanotubes, metal oxide nanofibers,metal oxide nanoparticles or metal oxide nanoplatelets or a combinationthereof The nanoreinforcements can be incorporated into the polymermatrix of the fiber during synthesis of the fiber matrix or processingof the matrix into fibers. For example, the nanoreinforcements can becombined with the neat polymer matrix prior to thermal processing intofibers. The nanoreinforcements can also be incorporated into themonomeric precursors used to synthesize the polymeric composition of thecloth fiber.

Graphene nanoplatelets are commercially available from sources such asXG Sciences, and can be prepared by mechanical and/or thermalexfoliation of graphite. Graphene nanoplatelets can be prepared invarious sizes, and those used in the barrier layer described herein canhave a thickness ranging from 2 nm to 50 nm, more particularly from 5 nmto 15 nm. The graphene nanoplatelets can have diameters ranging from 0.5μm to 50 μm, more particularly from 5 μm to 25 μm (note that diameter onthe hexagonal-shaped nanoplatelets is defined as the distance betweenopposite corners of the hexagon). As mentioned above, the barrier layercomprises at least 20 wt. % graphene nanoplatelets, based on the totalweight of the barrier layer (i.e., the cured coating). In some exemplaryembodiments, the barrier layer comprises at least 25 wt. % graphenenanoplatelets, and in some embodiments at least 30 wt. % graphenenanoplatelets. Upper limits of graphene nanoplatelet content in thebarrier layer in some embodiments can range up to 90 wt. %, in someembodiments up to 60 wt. %, and in some embodiments up to 35 wt. %. Inone exemplary embodiment, the barrier layer comprises about 30 wt. % ofgraphene nanoplatelets. The barrier underlayer and the barrier overlayercan optionally contain graphene nanoplatelets. When present in thebarrier underlayer and/or the barrier overlayer, the content levelgraphene nanoplatelets can comprise a minimum of 0.5 wt. %, in someembodiments a minimum of 1 wt. %. When present in the barrier underlayerand/or the barrier overlayer, the content level of graphenenanoplatelets have a maximum 5 wt. %, in some embodiments a maximum of 4wt. %, and in some embodiments a maximum of 3 wt. %. In one exemplaryembodiment, the barrier underlayer and the barrier overlayer comprisesabout 2 wt. % graphene nanoplatelets. In another exemplary embodiment,the barrier underlayer and the barrier overlayer has no graphenenanoplatelets. All weight percentages are based on the total weight ofthe respective coating layer.

The resin used for the barrier layer as well as the barrier underlayerand the barrier overlayer can be chosen from various polymers.Polyurethane polymers and polyurethane-containing copolymers are oftenused, at least in part due their elasticity and durability. Well-knownpolyurethane chemistry allows for various aromatic and/or aliphaticpolyisocyanates and polyols to be reacted together to provide desiredcoating characteristics, and such coating resins are readilycommercially available. Other polymers can be readily copolymerized withpolyurethanes, often through inclusion of hydroxy-terminated prepolymers(e.g., OH-terminated polyester or OH-terminated polycarbonate orpolyether) in the polyisocyanate/polyol reaction mix. In someembodiments, a polymer resin other than polyurethane is used, e.g.,polyester. Blends of one or more of polymer resins such as thosedescribed above can also be included in a coating composition.

The coating composition can also contain one or more crosslinkers. Forexample, urethane and polyester resins can include polyfunctionalalcohols (e.g., trimethylolpropane) or poly-functional alcohol reactivecompounds (e.g., melamine derivatives such as hexamethoxymethylolmelamine or melamine resin) as crosslinking agents. Polyurethane resinscan also include polyfunctional isocyanates (e.g., trifunctionalisocyanurate compounds formed by diisocyanates such as methylenediphenyldiisocyanate (MDI) or isophorone diisocyanate (IPDI)) as crosslinkers.Polyesters can also include polyfunctional acids (e.g., tricarballylicacid) as crosslinkers. The amount of crosslinker can be adjusted bythose skilled in the art to achieve desired properties. In addition toaccelerating cure, added crosslinker tends to increase coating hardnessand decrease elasticity. The coating composition may also contain one ormore volatile liquids, including water and/or various polar or non-polarorganic solvents. Such volatile liquids are vaporized before or duringcure and do not form part of the cured or finished coating. Reactivediluents (i.e., organic compounds that function as a solvent duringapplication of a polymer resin-containing coating composition, but havefunctional groups that react with the polymer during cure so that theyform part of the cured coating.

The coating compositions applied to form the any of the coatings on thefabric described herein can include various additives ordinarilyincorporated into coating compositions. Such additives can be mixed at asuitable time during the mixing of the components for forming thecomposition, and include fillers, reinforcing agents, antioxidants, heatstabilizers, biocides, plasticizers, lubricants, antistatic agents,colorants, surface effect additives, radiation light stabilizers(including ultraviolet (UV) light stabilizers), stabilizers, and flameretardants. Such additives can be used in various amounts, generallyfrom 0.01 to 15 wt. %, based on the total weight of the coatingcomposition

As mentioned above, in some embodiments, the barrier layer can includeone or more flame retardants. Exemplary flame retardants includephosphorous-containing compounds such as organophosphates (e.g.,tris(2-butoxy)ethylphosphate (TBEP), tris(2-propylphenyl)phosphate,organophosphonates (e.g., dimethylphosphonate), organophosphinates(e.g., aluminum diethylphosphinate), inorganic polyphosphates (e.g.,ammonium polyphosphate)), organohalogen compounds (e.g.,decabromodiphenyl ethane, decabromodiphenyl ether, and variousbrominated polymers or monomers), compounds with both halogen andphosphorous-containing groups (e.g., tris(2,3-dibromopropyl) phosphate),as well as other known flame retardants. Brominated flame retardants areoften used in combination with a synergist such as oxides of antimony(e.g., SbO₃, Sb₂O₅) and other forms of antimony such as sodiumantimonite. The amount of flame retardant can vary widely depending onthe particular flame retardant or combination of flame retardants, withexemplary amounts ranging from 5 wt. % to 50 wt. %, more particularlyfrom 10 wt. % to 25 wt. %.

Other coating layers can be present in addition the above-describedbarrier layer, barrier overlayer, and barrier underlayer. In someembodiments, a heat-resistant (HR) layer is also present, often on theside of the fabric that will be the outside of the inflatable structure.HR layers can comprise a high temperature polymer resin binder andaluminum pigment. HR layers can contain at least 10 wt. % aluminumpigment. An exemplary formulation contains between 0.1 wt. % and 10 wt.% microspheres. A further exemplary formulation contains between 1 wt. %and 5 wt. % microspheres. In addition to radiant heat reflectingproperties provided by the aluminum pigment, a heat-resistant layer canalso include heat-absorbing additives such as ceramic microspheres. HRlayers can contain at least 0.11 wt. % microspheres. An exemplaryformulation contains between 0.11 wt. % and 6.2 wt. % microspheres. Afurther exemplary formulation contains between 1.1 wt. % and 2.1 wt. %microspheres. All weight percentages are based on the total weight ofthe layer. Tie coat layers can also be present. Tie coats are utilizedto provide greater adhesion to the substrate than might be provided bythe various functional layers. For example, a polyurethane-polycarbonatecopolymer resin can be used in a tie coat applied directly to the fabricsurface where its relatively low modulus of elasticity provides goodconformation of the resin to the cloth morphology while the relativelyhigher modulus of elasticity of a polyurethane polymer resin used asbinder for a barrier layer, barrier underlayer, and/or barrier overlayerprovides the necessary strength and flexibility to maintain overallcoating integrity and air impermeability when subjected to deformationand stress during inflation.

Turning now to the figures, FIG. 1 schematically depicts a cross-sectionview of an exemplary air-impermeable fabric 100 according to theinvention. As shown in FIG. 1, fabric substrate 110 has barrierunderlayer 120 disposed thereon. Barrier layer 130 comprising at least20 wt. % graphene nanoplatelets is disposed over barrier underlayer 120.Barrier overlayer 140 is disposed over barrier layer 130. Barrier layer130 along with barrier underlayer 120 and barrier overlayer 140 aredisposed on one side of the fabric substrate 110 such as a side of thefabric that would be face the interior of an inflatable structure. Onthe other side of fabric substrate 110 is a heat-resistant layer 150such as an aluminized coating. The above arrangement provides airretention (AR) layers on one side of the fabric that can face theinterior of an inflatable structure and a heat-resistant layer 150 onthe other side of the fabric that would be the exterior of an inflatablestructure. This arrangement provides resistance to heat from externalsources such as fire on the outside of an inflatable structure whilekeeping the critical AR layers further away from such external heatsources. Of course, other layer arrangements can be used as well. Forexample, the AR layers could be disposed between the base fabric and anoutermost heat-resistant layer.

Turning now to FIG. 2, an inflatable evacuation slide assembly 10 isdepicted incorporating features of the present invention. Evacuationslide assembly 10 generally comprises a head end 12, and a foot end 14terminating at toe end 16. Head end 12 is configured to coupleevacuation slide assembly 12 to an exit door 18 of an aircraft 20 whilefoot end 14 is in contact with the ground 22 such that the slideassembly 10 provides a sloping surface to permit the rapid egress ofpassengers from aircraft 20.

With reference to FIGS. 2 and 3, the main body of evacuation slideassembly 10 comprises a plurality of inflatable flexible membersincluding side rail tubes 24, 26 which extend from head end trussassembly 28 to the ground 22. A slide surface 30 comprising a fabricmembrane is stretched between side rail tubes 24 and 26 to provide asliding surface for the disembarking passengers. A right hand rail 32and a left hand rail (not shown) are positioned atop side rail tubes 24and 26, respectively, to provide a hand hold for passengers descendingevacuation slide assembly 10. Head end truss assembly 28 comprises aplurality of strut tubes 36, 38, upright tubes 40, 42 and a transversetube 44 adapted to hold head end 12 of evacuation slide assembly 10against the fuselage of aircraft 20 in an orientation to permit escapeslide assembly 10 to unfurl in a controlled manner as it extends towardthe ground.

The spaced apart configuration of side rail tubes 24 and 26 ismaintained by a head end transverse tube 46, a toe end transverse tube48, a foot end transverse truss 52 and medial transverse truss 54. Thebending strength of escape slide assembly 10 is enhanced by means of oneor more tension straps 50 stretched from toe end 16 over foot endtransverse truss 52, medial transverse truss 54 and attached proximalhead end 12 of evacuation slide assembly 10. As described, evacuationslide assembly 10 provides a lightweight structure that consumes aminimum amount of inflation gas while providing the necessary structuralrigidity to permit passengers to safely evacuate an aircraft underemergency conditions.

The entire inflatable evacuation slide assembly 10 can be fabricatedfrom an air impervious material described more fully hereinafter. Thevarious parts of the inflatable evacuation slide assembly 10 may bejoined together with a suitable adhesive whereby the structure will forma unitary composite structure capable of maintaining its shape duringoperation. The entire structure of the inflatable evacuation slideassembly 10 can be formed such that all of the chambers comprising thestructure are interconnected pneumatically, such that a singlepressurized gas source, such as compressed carbon dioxide, nitrogen,argon, a pyrotechnic gas generator or combination thereof may beutilized for its deployment.

The invention is further illustrated by the following non-limitingexamples.

Examples

Fabrics prepared using a nanocomposite resin incorporating about 1.5weight % of graphene nanoplatelets were evaluated for radiant heatresistance. Sample A (4.87 oz./yd² estimated areal weight) had twoair-retentive layers having approximately 0.40 oz./yd² areal weighteach, and Sample B (5.97 oz./yd² estimated areal weight) incorporatedtwo air-retentive layers approximately 0.85 oz./yd² areal weight each.Additional samples were prepared using a resin mixture incorporating22.5 weight % graphene nanoplatelets, which was applied directly ontothe nylon fabric. This resin application was followed by an additionallayer of a nanocomposite resin incorporating 1.5 weight % graphenenanoplatelets. Sample C (5.10 oz./yd² estimated areal weight) wasselected from this group. All samples also have a radiant heat resistantcoating approximately 0.50 oz./yd² estimated areal weight. The sampleswere subjected to radiant heat testing according to ASTM F828-83, andthe results are shown in FIG. 4.

As shown in FIG. 4, the conventional sample (Sample B) maintained apressure above the minimum passing pressure of 3.5 psi throughout thetest, but required a relatively high areal weight of 5.97 oz/yd² to doso. The sample with two conventional coatings containing graphenenanoplatelets (Sample A) provide a low areal weight of 4.87 oz/yd², butfell below the minimum passing pressure after 240 seconds. However, thesample according to the invention (Sample C) maintained a pressure abovethe minimum passing pressure of 3.5 psi throughout the test, with areduced areal weight of 5.10 oz/yd².

As used herein, the singular forms “a,” “an,” and “the” include pluralreferents unless the context clearly dictates otherwise, and “or” means“and/or”. The modifier “about” used in connection with a quantity isinclusive of the stated value and has the meaning dictated by thecontext (e.g., includes the degree of error associated with measurementof the particular quantity). The terms “front”, “back”, “bottom”, and/or“top” are used herein, unless otherwise noted, merely for convenience ofdescription, and are not limited to any one position or spatialorientation. The endpoints of all ranges directed to the same componentor property are inclusive and independently combinable (e.g., ranges of“less than or equal to 25 wt %, or 5 wt % to 20 wt %,” is inclusive ofthe endpoints and all intermediate values of the ranges of “5 wt % to 25wt %,” etc.). The suffix “(s)” is intended to include both the singularand the plural of the term that it modifies, thereby including at leastone of that term (e.g., “the colorant(s)” includes a single colorant ortwo or more colorants, i.e., at least one colorant). “Optional” or“optionally” means that the subsequently described event or circumstancecan or can not occur, and that the description includes instances wherethe event occurs and instances where it does not. Unless definedotherwise, technical and scientific terms used herein have the samemeaning as is commonly understood by one of skill in the art to whichthis invention belongs.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. An air-impermeable fabric, comprising a fabric substrate; a barrierlayer comprising a first resin binder and graphene nanoplatelets, saidbarrier coating comprising at least 20 wt. % of the graphenenanoplatelets, based on the total weight of the barrier layer; and abarrier overlayer disposed on the opposite side of the barrier layerfrom the barrier underlayer, comprising a second resin binder.
 2. Theair-impermeable fabric of claim 1, further comprising a barrierunderlayer disposed between the barrier layer and the fabric, comprisinga third resin binder
 3. The air-impermeable fabric of claim 2, whereinthe barrier underlayer comprises from 0.5 wt. % to 5 wt. % of graphenenanoplatelets, based on the total weight of the barrier underlayer. 4.The air-impermeable fabric of claim 1, wherein the barrier overlayercomprises from 0.5 wt. % to 5 wt. % of graphene nanoplatelets, based onthe total weight of the barrier overlayer.
 5. The air-impermeable fabricof claim 2, wherein the barrier underlayer and the barrier overlayereach independently comprises from 0.5 wt. % to 5 wt. % of graphenenanoplatelets, based on the total weight of the barrier underlayer andthe barrier overlayer, respectively.
 6. The air-impermeable fabric ofclaim 1, wherein the barrier layer comprises from 20 wt. % to 90 wt. %of the graphene nanoplatelets, based on the total weight of the barrierlayer.
 7. The air-impermeable fabric of claim 1, wherein the barrierlayer comprises from 20 wt. % to 60 wt. % of the graphene nanoplatelets,based on the total weight of the barrier layer.
 8. The air-impermeablefabric of claim 1, wherein the barrier layer comprises from 25 wt. % to45 wt. % of the graphene nanoplatelets, based on the total weight of thebarrier layer.
 9. The air-impermeable fabric of claim 1, wherein thebarrier layer comprises from 25 wt. % to 35 wt. % of the graphenenanoplatelets, based on the total weight of the barrier layer.
 10. Theair-impermeable fabric of claim 1, wherein the barrier layer comprisesabout 30 wt. % of the graphene nanoplatelets.
 11. The air-impermeablefabric of claim 1, wherein the barrier layer further comprises aphosphorus-based flame retardant.
 12. The air-impermeable fabric ofclaim 1, wherein the barrier layer has a thickness of from 0.01 μm to 5μm.
 13. The air-impermeable fabric of claim 1, wherein the barrier layerhas a thickness of from 0.1 μm to 2 μm.
 14. The air-impermeable fabricof claim 2, wherein each of the barrier underlayer and the barrieroverlayer independently has a thickness of 0.5 μm to 20 μm.
 15. Theair-impermeable fabric of claim 1, further comprising a heat-resistantlayer disposed on the opposite side of the fabric substrate from thebarrier layer.
 16. The air-impermeable fabric of claim 15, wherein theheat-resistant layer comprises ceramic microspheres and/or aluminum in aresin binder.
 17. The air-impermeable fabric of claim 1, wherein thefabric substrate is subjected to calendaring compression prior todisposition thereon of the barrier layer, barrier underlayer, andbarrier overlayer.
 18. The air-impermeable fabric of claim 1, having anareal weight of less than or equal to 6 oz/yd² (170 g/m²).
 19. Aninflatable structure comprising the air-impermeable fabric of claim 1.20. The inflatable structure of claim 19 that is an aircraft evacuationslide.